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Old Mar 28, 2012, 05:44 PM
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Originally Posted by Dr.M View Post
How about a 3D foamy plank? certainly cheaper than a heli and will give you the opportunity to test the new features of the ZYX-S
I bought and built a Gee Bee 3D few months back. I have flown it once, but haven't got back to it yet.
Are you saying I can attach a ZYX to it?
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Old Mar 28, 2012, 06:08 PM
Track clear , smoke on !
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That's what it says.
It says it will do Quadcopters both (+) and (X) , fixedwing , and jet aircraft.

A foamie or in this case your Gee Bee would fall under the fixedwing class of aircraft , so give it a go and let us all know how it works.

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Old Mar 28, 2012, 06:21 PM
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Originally Posted by cap231ex View Post
That's what it says.
It says it will do Quadcopters both (+) and (X) , fixedwing , and jet aircraft.

A foamie or in this case your Gee Bee would fall under the fixedwing class of aircraft , so give it a go and let us all know how it works.

LOL, I will let you know.
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Old Mar 28, 2012, 06:32 PM
just gotta mess with it!
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Originally Posted by Dr.M View Post
How about a 3D foamy plank? certainly cheaper than a heli and will give you the opportunity to test the new features of the ZYX-S
Really Doc, using the P word on this thread!
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Old Mar 28, 2012, 08:17 PM
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Originally Posted by John_NZ View Post
I have ordered the ZYX-S and was sorely tempted to get another heli.
I have no idea why these things become some sort of addiction
that great man and addiction to this hobby is good one...

thank
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Old Mar 28, 2012, 09:28 PM
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Originally Posted by 2Doggs View Post
Really Doc, using the P word on this thread!
i know, right? *facepalm*
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Old Mar 29, 2012, 03:53 PM
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Originally Posted by asasan View Post
not really. it is actually the opposite. the servo and the gears will see more load if the "moment arm" is shorter (less leverage). The only positive is that when full range of servo travel is not utilized, shorter arm results in servo having to move more so you will have better resolution.

In any case, these are minor relative to the importance of having vertical links and orthogonal configuration the best you can.

Frankly, I am surprised and reluctant to believe shorter arm had positive effect on oscillations since they could also occur when in "perfect hands-free hover" (if there is such a thing) where servos are not even fully engaged. If oscillation is observed while in transition, then it most likely has to do with PID adjustments rather than servo arm length.
Sorry to bring this up, but my first statement still stands true, and its important that the readers understand, shorter arms are better except for very high pitch and very low pitch interactions, nearly all other things will benifit, as shown below

1) a shorter arm is more acurate, to the swashplate. Consider an arm at 10mm with 1mm of free play or gear train slack, at 20mm it would have 2mm of free play, basic engineering.

2) the geartrain of the servo, the servo motor, and associated electronics would see less apposing torque from the blades through the swash plate, engineering basic lever principals

3) the servo would indeed show the swash plate an improved resolution and centering acuracy

4) if three equal shorter arms are used, it will pull less amps than longer arms

5) longer arms are more prone to flutter and flex than shorter arms, and in certain circumstances, can amplify or mask gyro corrections , overshoots.

6) shorter arms can cope with higher gain settings.

But the down side of shorter arms is near max positive pitch and max negative pitch, there is a far bigger interaction problem when using roll and elevator control, this is typically seen by setting collective at centre stick 0 degs and use a pitch guage, measure full left or right roll blade angle, then move stick to full pitch and measure the same thing again, you will find it will be less, also if you measure both blades at full collective and full roll you will notice a small reduction in total pitch.


again i do apologise bringing this up but its important to know this when setting up CCPM get the best balance you can, use the shortest arm to get a fraction more than full throw required, if you really do need long arms, make sure you are using the best possible quality servo you can get, so until someone comes up with high quality linear servos, its the best we can do, i am totally surprised that no one has made these yet for CCPM control other than Eflite on its baby blade helis
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Old Mar 29, 2012, 06:52 PM
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you also lose some speed with shorter servo arms, but I agree the servos will see less load and perform better in the sense of (useful motion) / slop ratio.
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Old Mar 29, 2012, 07:15 PM
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Originally Posted by mike00top View Post
Sorry to bring this up, but my first statement still stands true, and its important that the readers understand, shorter arms are better except for very high pitch and very low pitch interactions, nearly all other things will benifit, as shown below

1) a shorter arm is more acurate, to the swashplate. Consider an arm at 10mm with 1mm of free play or gear train slack, at 20mm it would have 2mm of free play, basic engineering.

2) the geartrain of the servo, the servo motor, and associated electronics would see less apposing torque from the blades through the swash plate, engineering basic lever principals

3) the servo would indeed show the swash plate an improved resolution and centering acuracy

4) if three equal shorter arms are used, it will pull less amps than longer arms

5) longer arms are more prone to flutter and flex than shorter arms, and in certain circumstances, can amplify or mask gyro corrections , overshoots.

6) shorter arms can cope with higher gain settings.

But the down side of shorter arms is near max positive pitch and max negative pitch, there is a far bigger interaction problem when using roll and elevator control, this is typically seen by setting collective at centre stick 0 degs and use a pitch guage, measure full left or right roll blade angle, then move stick to full pitch and measure the same thing again, you will find it will be less, also if you measure both blades at full collective and full roll you will notice a small reduction in total pitch.


again i do apologise bringing this up but its important to know this when setting up CCPM get the best balance you can, use the shortest arm to get a fraction more than full throw required, if you really do need long arms, make sure you are using the best possible quality servo you can get, so until someone comes up with high quality linear servos, its the best we can do, i am totally surprised that no one has made these yet for CCPM control other than Eflite on its baby blade helis
I agree I got no. 2 backwards. To me, the rest are all the same root cause and effect based on better resolution and accuracy, with the exception of amp draw witch ties to no. 2.
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Old Mar 29, 2012, 08:02 PM
just gotta mess with it!
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Slop

But in order to minimise slop due to linkage tolerances, the general principle should be to use servo arms that are as long as possible.

With an FBL heli though, your optimum servo arm length will be determined by the length of the blade grip arms on the head, such that you end up with a collective range value around 60. That means you won't run short of servo travel when you combine maximum collective and cyclic inputs.
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Old Mar 29, 2012, 08:12 PM
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Originally Posted by 2Doggs View Post
But in order to minimise slop due to linkage tolerances, the general principle should be to use servo arms that are as long as possible.

With an FBL heli though, your optimum servo arm length will be determined by the length of the blade grip arms on the head, such that you end up with a collective range value around 60. That means you won't run short of servo travel when you combine maximum collective and cyclic inputs.
Unless the slop is in the servo, then the length of the servo arm is not going to be in that calculation is it?

Consider that if the servo arm was completely un-moveable by any amount of force, then the movement in the blade due to slop in the linkages etc is going to be identical regardless of where it is mounted on the servo arm. Or am I missing something in my thinking?
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Old Mar 29, 2012, 08:45 PM
just gotta mess with it!
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Of Arms and Slop

Quote:
Originally Posted by John_NZ View Post
Unless the slop is in the servo, then the length of the servo arm is not going to be in that calculation is it?
I deliberately didn't mention gear backlash, since, on any setup achieving the magic 60, the effects of that backlash in terms of the main blade angle change will be the same. So on a heli with blade grip arms 9mm long, using 6.5mm servo arms, and on one with 18mm grip arms, with 13mm servo arms, the servo backlash would give the same change in main blade angle.

Quote:
Originally Posted by John_NZ View Post
Consider that if the servo arm was completely un-moveable by any amount of force, then the movement in the blade due to slop in the linkages etc is going to be identical regardless of where it is mounted on the servo arm. Or am I missing something in my thinking?
You can see that the head with the 18mm arms will require twice as much servo travel as the one with 9mm arms - so a fixed amount of linkage slop will be twice as significant in the short arm head. It is independent of where the linkage ball is on the servo arm, but that position is pre-determined, within a fairly small range, by the blade grip arm length.

My RJX head, with giant 22mm arms, certainly seems more slop-free than my Tarot head with 18mm arms.
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Old Mar 29, 2012, 09:39 PM
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Originally Posted by 2Doggs View Post
I deliberately didn't mention gear backlash, since, on any setup achieving the magic 60, the effects of that backlash in terms of the main blade angle change will be the same. So on a heli with blade grip arms 9mm long, using 6.5mm servo arms, and on one with 18mm grip arms, with 13mm servo arms, the servo backlash would give the same change in main blade angle.
Ah, but that was my point, movement at the blade due to gear backlash is made worse by the length of the servo arm. If a servo has a gear backlash of theta degrees, then the amount of movement at the ball joint on the servo arm is R * sin(theta), where R is the length of the servo arm. The greater R is, the more movement at the ball.
So with a sloppy servo a longer servo arm length is going to mean more movement at the blade than with the short servo arm.
With the slop in the joints from that point on, only the interim lever arm lengths have any influence on the movement and their lengths are all fixed.

And yes, a head with 18mm arms will not be as sensitive to the slop in the joint as a head with 9mm arms will be, as this is the opposite to the servo arm length issue. That is, if the slop is x units at the head arm ball, then the amount of rotation of the blade is arcsin(x/H) where H is the head arm length. So the longer the head arm, the less rotation of the blade.

So in other words, as I see it, if you want to minimize the effect of servo backlash, loose ball joints etc in terms of the unwanted rotation in the blades, then you want long head arms and short servo arms.
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Old Mar 29, 2012, 09:47 PM
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All the references to dimension of head arm or grip arm are width or distance from the ball to the center of main shaft in transverse direction and not length of the arm parallel to the blades, right? Otherwise, length of that arm is immaterial.
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Old Mar 29, 2012, 09:51 PM
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Originally Posted by asasan View Post
All the references to dimension of head arm or grip arm are width or distance from the ball to the center of main shaft in transverse direction and not length of the arm parallel to the blades, right? Otherwise, length of that arm is immaterial.
Yes.
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